1. Field of the Invention
The present invention is broadly concerned with liquid feed supplements of the type which include a starch source and a nonprotein nitrogen (NPN) substance such as urea. More particularly, it is concerned with the method of making such NPN fortified supplements which requires a minimum of processing equipment, can accommodate a wide variety of differing processing techniques, and which yields final products having superior protein synthesis and growth-inducing properties.
2. Description of the Prior Art
It has long been known that NPN substances such as urea may be incorporated into feed for ruminants as a replacement for protein sources therein. When fed, the urea is first degraded by rumen microorganisms to ammonia, and a portion of the latter is then converted to microbial protein. A major portion of such microbial protein is then enzymatically degraded to amino acids in the small intestine of the ruminant, where, after being absorbed, they are available for use by the animal. Thus, NPN supplementation provides an economically attractive method of providing protein for the ruminant.
However, it has also long been known that NPN substances can be toxic to the ruminant if directly fed in more than relatively minimal amounts. Therefore, although direct feeding of NPN substances is a known practice, use of this technique is somewhat limited because of the inherent toxicity problems.
U.S. Pat. No. 3,642,489 describes chunk-type products which are produced through an extrusion process wherein a starch bearing food source such as corn and an NPN substance such as urea are admixed and run through a cooker-extruder to give a chunk-type product. Experience has proven that use of this type of process permits use of the NPN substance at levels which would be extremely toxic if simply mixed with a raw starch source and fed directly.
It is of significance that during experimentation in connection with extrusion produced products in accordance with U.S. Pat. No. 3,642,489, it was discovered that it was essential to add the NPN substance to the starch bearing material initially, whereupon this starch-NPN admixture was extruded. Attempts to add urea subsequent to the extrusion of an NPN-free starch source proved ineffective in giving an equivalent product.
Liquid starch-NPN food supplements are also known. For example, U.S. Pat. No. 3,988,483 described such a product which is produced using a jet cooker wherein a slurry comprising water, a starch bearing food substance, and an NPN source are admixed and run through a jet cooker for turbulent heating and gelatinization of the starch bearing material in the presence of the NPN source.
It is also known to prepare sprayable liquid feed supplements which include a minor amount of a starch source such as wheat or corn in conjunction with urea. For example, U.S. Pat. No. 3,684,518, describes a method wherein an aqueous slurry of wheat flour and urea liquor is prepared and simply heated at atmostpheric pressure in order to provide a liquid product which is resistant to sedimentation. In addition, U.S. Pat. No. 3,653,909, describes a method wherein melamine and urea are admixed in aqueous suspension with wheat flour and heated under atmospheric pressure to achieve a uniform consistency. Other patents of background interest include: U.S. Pat. Nos. 3,968,253, 4,006,253, 4,016,296, 3,937,846, 3,852,498, 3,490,912, 3,635,725, 4,017,642, 4,044,156, 3,573,924, 3,165,413, 2,853,385, 2,748,001, 2,960,406, and 3,677,767.